Field of the Invention
The invention relates to a method for controlling a quantity of ink in an inking unit of a printing machine using a predetermined nominal or desired value.
For metering ink into the inking unit of a printing machine, ink fountains or ducts have become known heretofore which include a fountain or duct roller, also called a ductor, that rotates in contact with fluid ink and a number of doctor blades disposed adjacent one another in the longitudinal direction of the fountain roller, the positioning of the doctor blades at the fountain roller being controllable by actuators, so that the doctor blades adjust the thickness of the ink layer, which is removed from the ink bath by the fountain roller, to a separately definable value for each individual zone.
A vibrator roller performs an oscillating movement wherein, in a first end position thereof, it engages the fountain roller in such a way that the ink layer located thereon is transferred to the vibrator roller, and in a second end position thereof, it engages an inking unit roller so as to transfer the ink portion that is picked up by the fountain roller, onto the inking unit roller.
The ink flow, i.e., the quantity of ink per unit of time, with which the inking unit is supplied, thus derives from the number of ink portions that are transferred per unit of time, and the size of each individual ink portion is determined by the thickness of the ink layer on the fountain roller (which may differ from zone to zone) and the size of the portion of the surface area of the vibrator roller that comes into contact with the fountain roller in the course of a cycle of the oscillating motion.
In the context of supplying ink to individual zones of the inking unit of a printing machine, it has been known heretofore always to overcontrol the ink supply of the affected zone when the ink quantity in this zone is changed. This means that when the desired quantity of ink for the zone is changed, the thickness of the ink layer that is appropriate in order to maintain the desired ink quantity in continuous operation is not immediately set on the fountain roller; rather, when the modification calls for an increase or a reduction of the ink quantity, a temporary value of the ink layer thickness is initially set, which is larger and smaller, respectively, than that which would be required in order to maintain the desired ink quantity in continuous operation.
But this method only functions when the desired modification of the ink quantity, including the overcontrol, can be achieved by adjusting the layer thickness on the fountain roller, for example, by an electronic ink zone control such as the aforementioned control of the positioning of the doctor blades against the fountain roller.
It is accordingly an object of the invention to provide a method for controlling an ink quantity in an inking unit by which it is also possible to make very large adjustments in the ink quantity within a short time period. Another object of the invention is to provide such a method by which an acceleration of the inking unit response is achieved, even when the ink fountains are without electronic ink zone control.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for controlling the ink quantity in an inking unit of a printing machine by a predetermined nominal value, using a vibrator roller oscillating between a fountain roller and the inking unit, and picking up an ink portion and surrendering it to the inking unit with which the vibrator roller is in contact, which comprises varying the width of an ink stripe on the vibrator roller, depending upon the nominal value, by adjusting the size of the transferred ink portion, for a modification in the nominal value, from a size (FI) corresponding to the nominal value prior to modification, to at least one intermediate size (Fz) lying beyond a size (Fx) corresponding to the modified nominal value and, subsequent to the expiration of a transition time interval ([t1,t2]), adjusting the intermediate size (Fz) of the ink portion back to the size (Fx) thereof corresponding to the modified nominal value.
In accordance with another mode of the method, the difference (Fu) between the intermediate size (Fz) and the size (FI) corresponding to the nominal value prior to the modification thereof is proportional to the difference between the size (FI) corresponding to the nominal value prior to modification thereof and the size (Fx) corresponding to the modified nominal value.
In accordance with a further mode of the method, the proportionality factor is between 1.5 and 2.5.
In accordance with an added mode, the method invention includes modifying the width of the ink stripe so as to adjust the ink portion between the size (Fx) corresponding to the modified nominal value and the intermediate size (Fz).
In accordance with an additional mode, the method includes modifying the thickness of the ink layer on the ink stripe so as to adjust the ink portion between the size (Fx) corresponding to the modified nominal value and the intermediate size (Fz).
In accordance with yet another mode, the method includes zonally controlling the thickness of the ink on the ink stripe.
In accordance with yet a further mode, the method includes zonally prescribing the ratio of the difference between the intermediate size (Fz) and the size (FI) corresponding to the nominal value prior to the modification, to the difference between the size (FI) corresponding to the nominal value prior to modification and the size (Fx) corresponding to the modified nominal value.
In accordance with yet an added mode, the method includes prescribing the ratio smaller, the larger the area is that is covered by the zone that is being controlled.
In accordance with yet an additional mode, the method includes modifying the duration of contact between the fountain roller and the vibrator roller so as to modify the width of the ink stripe.
In accordance with a concomitant mode, the method includes modifying the rate of rotation of the fountain roller so as to modify the width of the ink stripe.
It has proven expedient herein to select the difference between the temporary size of the ink portion and the size that corresponds to the nominal value prior to modification so as to be proportional to the difference between the size of the ink portion corresponding to the nominal value prior to modification and the size of the ink portion corresponding to the modified nominal value. The proportionality factor preferably is between 1.5 and 2.5. This means that the temporary size is overcontrolled compared to the size corresponding to the modified nominal value by a factor of 1.5 to 2.5.
While the modification of the ink portion from the size thereof corresponding to the nominal value prior to modification to the corresponding size thereof subsequent to modification is always accomplished by varying the width of the ink stripe, there are two logical methods for changing the size of the ink portion between the size corresponding to the modified nominal value and the temporary size. The first provides for a modification of the width of the ink stripe on the vibrator roller; i.e., the length along which the fountain roller and the vibrator roller engage one another in the course of a movement cycle of the vibrator roller is varied. This possibility also exists in machines with ink fountains without zonal control of the ink blades. The other possibility is to vary the thickness of the ink stripe that is transferred by the vibrator roller, so that, given a constant width of the ink stripe, portions of varying sizes can be transferred. Modification of the thickness is expediently accomplished by adjusting doctor blades that rest at the fountain roller, which determine the thickness of the ink layer that the fountain roller extracts from an ink fountain. This alternate embodiment can advantageously be used with ink fountains having zonally controllable blades.
It is particularly advantageous here, if the thickness of the ink stripe is controlled zonally. This makes it possible to stipulate the extent of the overcontrol separately for each zone and, for example, to select a greater overcontrol factor for a zone with a small area coverage compared to zones with larger area coverage.
Of course, the two aforementioned possibilities for modifying the size of the ink portion can also be combined. Thus, for example, it is imaginable that both the thickness of the ink stripe and the width are varied in an individual adjustment of the ink portion from the size corresponding to the modified nominal value to the temporary size, or the reverse. It would also be conceivable to perform an adjustment from the size corresponding to the modified nominal value to the temporary size by changing the width, and to perform the counteradjustment in the opposite direction by varying the thickness of the ink stripe, or the reverse, if this simplifies the control or proves otherwise expedient.
The width of the ink stripe can be influenced by shortening or lengthening the phase within the movement cycle of the vibrator roller wherein the vibrator roller is in contact with the fountain roller. Manipulation of the rate of rotation of the fountain roller is a particularly advantageous way to modify the width of the ink stripe, because this is easy to control. In this case, the width of the ink stripe that is generated on the vibrator roller during a constant contact period is approximately directly proportional to the rate of rotation of the fountain roller. The rate of rotation of the fountain roller can be selected quite freely, without having any effect on the functioning of the inking unit that is connected downline.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as a method for controlling a quantity of ink in an inking unit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific modes of the method when read in connection with the accompanying drawings, wherein: